Given a non-negative index k where k ≤ 33, return the kth index row of the Pascal’s triangle.
Note that the row index starts from 0.
In Pascal’s triangle, each number is the sum of the two numbers directly above it.
Example:
Input: 3
Output: [1,3,3,1]
Solution
我们首先确定一下最后返回的列表里有rowIndex + 1个数，而且第一个元素是1， 可以先初始化一个列表[1,0,0,0,0] 0的个数等于rowIndex， 然后循环rowindex次，每一次从最后一个元素开始计算。
i = 0
row[0] =1
j从1(i+1)开始递减， 计算row[1] = row[1] +row[0]= 1+0=1
此时 row的结果为[1,1,0,0,0]
接下来i=1
j从2到0递减，先计算row[2]=row[2]+row[1] = 0+1 =1
然后计算row[1] = row[1] +row[0] = 1 + 1 =2
row[0]不计算，还是1，退出内层循环，此时 row的结果为[1,2,1,0,0]
同理，i=2后 row的结果为[1,3,3,1,0]
i=3后 此时 row的结果为[1,4,6,4,1]
class Solution:
def getRow(self, rowIndex: int) -> List[int]:
row = [1] + [0] * rowIndex
for i in range(rowIndex):
row[0] = 1
for j in range(i+1,0,-1):
row[j] = row[j] +row[j-1]
return row
